in the military art, a small fortified place, environed on all sides with a moat, rampart, and parapet. Its use is to secure some high ground or the passage of a river, to make good an advantageous post, to defend the lines and quarters of a siege, &c.

Forts are made of different figures and extents, according as the ground requires. Some are fortified with battlements, others with demi-battlements. Some again are in form of a square, others of a pentagon. A fort differs from a citadel, as this last is built to command some town.